An example of a conventional portable navigation device is a device disclosed in Patent Reference 1. A system that includes a conventional portable navigation system is formed with a portable navigation device such as a portable telephone device to display a map on its display unit, a database for storing map data and road link information necessary for route searches, a map server that carries out route searches and creates route guide maps, and a communication network that connects the portable navigation device and the map server.
Next, an operation to be performed by a conventional portable navigation device is described. When a user inputs a departure point and a destination point to the portable navigation device and issues an instruction to search for a route, the portable navigation device sends the departure point and the destination point to the map server and issues a route search request via the communication network. The map server uses the road link information stored in the database, to perform a route search. The map server then determines the total length of the links forming the searched route, and sets the total length as the distance to the destination point. The map server next uses the map data stored in the database and the route search results, to create a route guide map that includes information about the departure point, the destination point, and the route on a map. The route guide map and the distance to the destination point are transmitted to the portable navigation device via the communication network, and are then displayed on the portable navigation device.
Next, an example display of a route guide map on a conventional portable navigation device is described. For example, a JR station is set as a departure point S, and a library is set as a destination point G. The route between the departure point S and the destination point G is indicated by a thick solid line, and landmarks existing along the route are denoted by numbers such as 1, 2, and 3 on the map. Explanation of those numbers and the distance to the destination point are also displayed on the map. With this arrangement, routes can be clearly displayed even on a small screen of a conventional portable navigation device, and it is possible to know the distance to each destination point.
Patent Reference 1: Japanese Patent Application Laid-Open No. 2001-4384